RANDOLPH — Jacob Kubel is a man on a mission. The 36-year-old conservation scientist with the Massachusetts Division of Fisheries and Wildlife’s Natural Heritage and Endangered Species Program has been crisscrossing the state since late August in search of the Commonwealth’s rarest salamander — Ambystoma opacum, also known as the marbled salamander — to document where it is breeding and to get a feel for how the population is doing. And he only has a couple more weeks to do so before the salamanders head back underground.

“I feel like I can’t stop searching for these guys while I have a hot hand,” Kubel said recently, about his luck thus far in finding the elusive amphibians. With the help of others — including personnel from the Division of Fisheries and Wildlife and the state Department of Conservation and Recreation, as well as academic institutions, land trusts, other nongovernmental organizations, and biologists in the private sector, he has documented marbled salamanders from Bolton to New Bedford, Attleboro to Berlin, and several places in between.

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Kubel has surveyed 62 wetlands and found 18 marbled salamanders distributed among 13 wetlands in nine cities and towns this season. He said other biologists have found five. But there is not enough data to estimate how many salamanders are in each local population.

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Statewide, Kubel said there are records of approximately 83 local populations, occurring in 78 of the state’s 351 towns, that have been observed in the past 25 years.

Marbled salamanders are unusual because they are fall breeders. In the springtime, vernal pools — temporary small ponds that form from spring rains and melting winter snow — are alive with an assortment of mating frogs, toads, and salamanders. By late summer these ephemeral woodland pools lie empty and devoid of most animal life, save for a few insects and other invertebrates. That is when the marbled salamander — in contrast to its spring-breeding counterparts — makes its way to these dried-out depressions to mate and lay eggs.

But finding the stocky-bodied 4-inch-long creatures can be a bit like finding the proverbial needle in a haystack. Kubel and fellow biologist Tim Beaulieu recently set out to search for them in the Blue Hills Reservation, a 7,000-acre state park just south of Boston.

“We’ve been tending to find one salamander per pool this year,” Kubel said. “If we find a marbled salamander, we say we found it, as opposed to saying we found one.”

In the Randolph section of the park, Kubel and Beaulieu headed down a trail through woods that led to vernal pools where the amphibians had been documented in the past.

“This looks like a good spot,” Kubel said, pointing to a large depression with a muddy bottom and scattered clumps of grass, shrubs, and fallen leaves. “There’s got to be marbled salamanders in here.”

He said the primary purpose of the survey in the Blue Hills, and across the state, is to confirm the continued presence of the species at previously known locations and to learn more about the possible distribution of marbled salamanders and their breeding sites.

“Do you have your search image?” he asked Beaulieu. “They’re black and white, so they’re pretty easy to spot if you uncover one.”

That distinctive black-and-white color pattern is what gives the marbled salamander its name. Males and females have similar markings, but males are brighter than females, a phenomenon that scientists refer to as sexual dichromatism.

“They’re interesting animals,” said Kubel. “They live underground about 10 months of the year, so they’re kind of mysterious, and there’s only a limited opportunity to see them.”

In fact, Kubel said his initial interest in herps — reptiles and amphibians — in general, and salamanders in particular, sprang from their secretive nature.

“It’s like a big treasure hunt,” he said. “I liked the satisfaction of putting effort into searching, and then finding something. Herps are elusive, so it makes you want to learn about them.”

Recent marbled salamander discoveries in Massachusetts have all been in communities south and west of Boston. Kubel said there are a number of historic records of the species north of Boston, most in the late 1800s and early 1900s, with the most recently confirmed record from 1932 in Malden.

“In most cases, the habitat is now gone,” he said, “so the populations are presumed to have been extirpated. Some people are still hopeful they remain at Middlesex Fells [a conservation area that straddles Medford, Malden, Melrose, Stoneham, and Winchester], but surveys to date have been unsuccessful there.”

Because of their relative scarcity in the state, marbled salamanders are protected in Massachusetts and listed as “threatened,” just one level above endangered, under the Massachusetts Endangered Species Act. They are near the northern limits of their distribution here, which is a contributing factor to their rarity, said Kubel. Marbled salamanders are more common in the southern and western parts of their range, which extends from Texas to Florida, and northward into southern New Hampshire.

“You need to get down on your hands and knees and carefully sift through clumps of dead leaves,” said Kubel. “I haven’t found any males for over a week, so the mating season is probably over. What we’re looking for now are females guarding their nests.”

The female marbled salamander generally lays between 50 and 150 eggs in a nest under a log, dead leaves, or other protective covering within a dried-out vernal pool. She curls her body around the eggs to protect them, and stays in the nest until the pool fills with water. The eggs usually hatch a few days after the nest is inundated.

Kubel added that some scientists think the presence of females at the nest might help prevent fungi from attacking the eggs, although more research needs to be done to confirm that.

He said if it is a dry fall and the pools do not fill with rain, the female will eventually abandon her eggs and head underground for the winter, either when it gets too cold or too dry, or if she is disturbed by a predator like a skunk or raccoon.

As for their unusual fall breeding behavior, Kubel said biologists speculate that the larvae of marbled salamanders may gain a competitive edge over their larger spring breeding cousins — spotted, blue spotted, and Jefferson salamanders — by laying their eggs when no competing species are around. The eggs typically hatch later in October or early November, and the marbled salamander larvae will then have several months to get a head start on the competition, growing large enough to feed on spring-breeding salamander larvae in addition to aquatic insects.

When not breeding, adult marbled salamanders spend most of their time underground or hiding beneath debris like stones and logs in their woodland homes. They feed on small invertebrates such as insects, slugs, and earthworms, and are active mainly at night. They produce a nasty-tasting milky secretion from their tails that may help protect them from predators like snakes and mammals.

Threats to the marbled salamander include destruction of vernal pools and upland habitat through development, as well as road traffic and chemical pollution of breeding sites. To protect the species, the Natural Heritage and Endangered Species Program recommends safeguarding vernal pools and their surrounding woodland habitat. It also encourages Massachusetts citizens to report marbled salamander sightings, as populations of these secretive animals tend to be small and localized, and many probably remain undiscovered.

“Monitoring the distribution of marbled salamanders across the landscape is one way to help determine whether populations are declining, improving, or holding steady,” Kubel said in an e-mail. “Since our environment is subject to continual change, and we do not fully understand all the factors that can influence population abundance and distribution, it is important to keep tabs on our populations at regular intervals.”

In the Blue Hills, after three hours of crawling around on their hands and knees in the mud, sifting through dead leaves, Kubel and Beaulieu did not find a single marbled salamander, so they ventured into another part of the park to search a previously documented breeding site where marbled salamanders had not been recorded since the mid-1990s. They found a lone female guarding her eggs in a dry vernal pool that afternoon.

Kubel said he will be back in the field in the spring, this time to look for marbled salamander larvae, explore for new populations, and monitor existing sites for new data.

“It’s exciting to find new populations of rare species,” he said. “It’s nice to know a species is more secure than we thought, but we can’t conclude that until we do the work. People expect that from us, that we’ll be out there doing the best we can to determine what the needs are for the species.”